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Abstract

Growth factor gene therapy is a new, promising tool for treatment of myocardial ischemia. Development of safe and effective clinical applications requires optimal selection of growth factors and knowledge of the mechanisms involved. We have previously discovered that adenovirally over-expressed (Ad) VEGF-B186 induces tissue-specific angiogenesis in the myocardium. Another VEGFR-1 specific ligand, placental growth factor (PlGF) induced angiogenesis both in the heart and skeletal muscle. We hypothesized that these two VEGFR-1 ligands utilize different angiogenic mechanisms. Unlike PlGF, the effect of VEGF-B was not dependent on the up-regulation of endogenous VEGF-A since soluble decoy VEGFR-2 did not block the effect. In contrast to PlGF or VEGF-A, the therapeutic effect of VEGF-B was not blocked by inhibition of nitric oxide synthesis by feeding the animals L-NAME, indicating that a novel angiogenic pathway was involved. Western blot (WB) analysis of the transduced tissues showed that in the myocardium AdVEGF-B186 was proteolytically processed, while majority of the protein in the skeletal muscle was unprocessed. Processed form of VEGF-B binds to another angiogenic receptor neuropilin-1 (Nrp-1). Immunohistochemical staining and WB showed strong Nrp-1 expression in the myocardium while Nrp-1 expression was below detection limit in the skeletal muscle. In addition, down-stream molecules GIPC and GAIP were co-localized with Nrp-1 suggesting Nrp-1 receptor activation. Co-transduction with soluble decoy AdsNrp-1 or AdsVEGFR-1 blocked the angiogenic effects of VEGF-B186 in the myocardium indicating that both receptors are involved in the angiogenic pathway. VEGF-B induces angiogenesis in the myocardium via VEGFR-1 and Nrp-1. This novel myocardium-specific angiogenic pathway offers a safe tool for growth factor therapies and provides new information about repair mechanisms of the heart.